Investigation of breed differences in plasma adrenocorticotropic hormone concentrations among healthy horses and ponies.

Plasma adrenocorticotropic hormone (ACTH) concentration is commonly measured to diagnose pituitary pars intermedia dysfunction (PPID). Several intrinsic and extrinsic factors affect ACTH concentrations, including breed. The objective of this study was to prospectively compare plasma ACTH concentrations among different breeds of mature horses and ponies. Three breed groups comprised Thoroughbred horses (n = 127), Shetland ponies (n = 131) and ponies of non-Shetland breeds (n = 141). Enrolled animals did not show any signs of illness, lameness or clinical signs consistent with PPID. Blood samples were collected 6 months apart, around the autumn equinox and spring equinox, and plasma concentrations of ACTH were measured by chemiluminescent immunoassay. Pairwise breed comparisons within each season were performed on log transformed data using the Tukey test. Estimated mean differences in ACTH concentrations were expressed as fold difference with 95 % confidence intervals (CI). Reference intervals for each breed group per season were calculated using non-parametric methods. In autumn, higher ACTH concentrations were found among non-Shetland pony breeds compared with Thoroughbreds (1.55 fold higher; 95 % CI, 1.35-1.77; P < 0.001), and in Shetland ponies compared with Thoroughbreds (2.67 fold higher; 95 % CI, 2.33-3.08; P < 0.001) and non-Shetland pony breeds (1.73 fold higher; 95 % CI, 1.51-1.98; P < 0.001). In spring, no differences were identified among breed groups (all P > 0.05). Reference intervals were similar among breed groups in spring, but upper limits for ACTH concentrations were markedly different between Thoroughbred horses and pony breeds in autumn. These findings emphasise that breed should be accounted for when determining and interpreting reference intervals for ACTH concentrations among healthy horses and ponies in autumn.

A survey of veterinarians' practices, recommendations and perceptions associated with the prevention of tetanus in horses in Australia.

OBJECTIVE: Identify veterinarians' practices, recommendations and perceptions when preventing tetanus in horses in Australia. METHODS: Graduated members of Equine Veterinarians Australia participated in an online survey about the prevention of tetanus in horses in Australia. RESULTS: Of 77 respondents (response rate ~ 8%), 50 (65%) reported that they had attended collectively 145-152 cases of tetanus in horses in Australia (1.1 cases of tetanus observed/10 veterinarian-years since qualification). The estimated case fatality rate (CFR) was at least 79%. Puncture wounds were most frequently suspected as the entry point (32%; n = 47). Five respondents (7%) reported cases of localised tetanus. Three respondents reported generalised tetanus within 2 weeks of tetanus antitoxin (TAT) administration. Respondents did not report any cases of tetanus in horses which had been vaccinated according to manufacturer's recommendations. All respondents recommended vaccination, but over 50% (N = 45) stated 'lack of veterinary recommendation' as often or sometimes a reason why clients did not vaccinate horses. Opinions varied on the use of TAT for peri-exposure prophylaxis; 67% of respondents dosed TAT independent of body weight, with the rest dosing according to body weight. Cases of Theiler's disease related to the use of TAT were not reported in Australia by respondents. DISCUSSION: The caseload of equine tetanus appears relatively low among equine veterinarians in Australia. Consistent with the literature, estimated CFR was high. Respondents' recommendations and perceptions about tetanus vaccination were generally consistent but varied regarding TAT usage. Evidence for TAT usage is limited and we recommend studies of TAT efficacy in horses.

Chlamydia psittaci: a suspected cause of reproductive loss in three Victorian horses.

Chlamydia psittaci was detected by PCR in the lung and equine foetal membranes of two aborted equine foetuses and one weak foal from two different studs in Victoria, Australia. The abortions occurred in September 2019 in two mares sharing a paddock northeast of Melbourne. The weak foal was born in October 2019 in a similar geographical region and died soon after birth despite receiving veterinary care. The detection of C. psittaci DNA in the lung and equine foetal membranes of the aborted or weak foals and the absence of any other factors that are commonly associated with abortion or neonatal death suggest that this pathogen may be the cause of the reproductive loss. The detection of C. psittaci in these cases is consistent with the recent detection of C. psittaci in association with equine abortion in New South Wales. These cases in Victoria show that C. psittaci, and the zoonotic risk it poses, should be considered in association with equine reproductive loss in other areas of Australia.

Serological responses of Australian horses using a commercial duplex indirect ELISA following vaccination against strangles.

OBJECTIVE: To determine the nature of serological responses in Australian horses using a commercial duplex indirect ELISA (iELISA) following vaccination against strangles. DESIGN: A group (n = 19) of client-owned horses from five properties were recruited to receive a primary course of a Streptococcus equi subsp. equi (S. equi) extract vaccine. Serological responses were determined by duplex iELISA incorporating S. equi-specific fragments of two cell wall proteins, SEQ2190 and SeM (antigens (Ag) A and C, respectively). METHODS: The horses were administered a primary strangles vaccination course. Blood was collected immediately prior to each of the three vaccinations at 2-week intervals and additionally at 28 and 56 days following the 3rd vaccination (V3). RESULTS: Significant increases in mean antibody levels of horses following vaccination were limited only to AgC, which was significantly increased at T2/V3, 14 days following V2 (ratio of geometric means = 3.7; 95% confidence interval (CI): 1.6, 8.4; P = 0.003). There was no increase in mean antibody to Ag A (ratio of geometric means = 1.4; 95% CI: 0.6, 3.2; P = 0.39). Four horses (22%) exceeded the test cut-off for AgC following vaccination. CONCLUSION: Vaccination of Australian horses is unlikely to interfere greatly with detection of strangles using the duplex iELISA. No responses would be anticipated to AgA following vaccination with Equivac© S/Equivac© 2in1 and only a minority are likely to respond to AgC. We conclude that the results of this study validate the usefulness of the duplex iELISA to assist control measures for strangles outbreaks in Australian horse populations.

Chronic phalaris toxicity in eastern grey kangaroos (Macropus giganteus).

CASE REPORT: Seven eastern grey kangaroos (Macropus giganteus) grazing pastures including Phalaris spp. in Victoria showed neurological deficits characterised by ataxia, head tremors and collapse. Gross examination of the brains and spinal cords of affected kangaroos showed a greenish discolouration in several regions of the grey matter. Histologically, intracytoplasmic accumulation of pigment granules was detected in the neurons, most prominently in the thalamus, brainstem and ventral horns of the spinal cord. Pigment granules were positive to stains used for identification of melanin, including Fontana-Masson stain and Schmorl's reaction. CONCLUSION: The combination of clinical signs and obvious neuronal pigmentation is consistent with chronic Phalaris spp. toxicity, a condition well documented in domestic ruminants.

Accelerated vaccination schedule provides protective levels of antibody and complete herd immunity to equine influenza.

REASONS FOR PERFORMING STUDY: During the 2007 Australian equine influenza (EI) outbreak, an accelerated primary course 14 day intervaccination schedule was proposed, but not widely implemented. Expert opinion was divided as to the efficacy of such a schedule given the lack of published data. This study determined the level and duration of humoral immunity following administration of a recombinant canarypox-vectored vaccine (ALVAC-EIV) with a primary intervaccination interval of 14 days and booster at 105 days. OBJECTIVES: To examine whether protective levels of immunity of adequate duration were achieved following a primary course reduced from a minimum interval of 28 to 14 days. Antibody responses to 2 H3N8 American lineage virus strains (including A/equine/Sydney/6085/2007) were assessed and compared to previous challenge studies using ALVAC-EIV at conventional intervaccination intervals. METHODS: Fourteen Thoroughbred horses and 2 ponies from a rural racehorse training property in Victoria, Australia, were vaccinated with ALVAC-EIV on Days 0, 14 and 105. Serial blood samples were collected over the next 32 weeks and tested with haemagglutination inhibition and single radial haemolysis (SRH) in full assays to evaluate the serological response. RESULTS: All horses and ponies responded to the accelerated ALVAC-EIV vaccination schedule. Mean SRH antibodies remained above those consistent with clinical protection for the duration of the study period. All vaccinates demonstrated high SRH antibodies 14 days following V2, thereby achieving 100% herd immunity to homologous viral challenge. CONCLUSIONS: An accelerated vaccination schedule conferred long-lasting protective antibody levels despite a >50% reduction in the recommended V1-V2 interval. POTENTIAL RELEVANCE: High levels of rapidly acquired herd immunity are critical in containing an outbreak of such a highly contagious pathogen as EIV. In a strategic vaccination programme, it is important that horses remain protected for sufficient time to allow control programmes to succeed. An accelerated 14 day primary course intervaccination interval and booster at 105 days achieves both of these objectives.

Murray Valley encephalomyelitis in a horse.

A 5-year-old Thoroughbred mare presented with signs of severe pain and was taken to exploratory laparotomy based on suspicion of an acute abdominal lesion. A mild gastrointestinal lesion was discovered, but was considered disproportional to the severity of signs displayed. The mare was later euthanased because of intractable pain. Comprehensive postmortem examination, including polymerase chain reaction testing of central nervous system tissue samples, allowed a definitive diagnosis of Murray Valley encephalomyelitis to be made. This case demonstrates the variability of clinical presentations in horses infected with Murray Valley encephalitis virus.

Evaluation of the response to an accelerated immunisation schedule using a canarypox-vectored equine influenza vaccine, shortened interdose intervals and vaccination of young foals.

The results of an accelerated immunisation schedule for horses used as part of the emergency response plan to contain and eradicate equine influenza in Australia in 2007 is described. The horses studied were vaccinated with a recombinant canarypox-vectored vaccine (ProteqFlu®, Merial) with a shorter interdose interval. Vaccinated horses included foals aged less than 4 months.

Circulating angiotensin converting enzyme in endurance horses: effect of exercise on blood levels and its value in predicting performance.

REASONS FOR PERFORMING STUDY: Investigate angiotensin converting enzyme (ACE) activity in equine plasma as a predictor of performance in endurance competitions and the effect of endurance exercise on ACE activity. HYPOTHESIS: Precompetition values of ACE activity in equine blood are correlated with performance results and with heart rates pre- and post competition used as indicators of fitness. Endurance exercise increases ACE activity. METHODS: Nineteen horses participating in an 80 km endurance competition had venous blood samples collected before and after the ride. ACE activity and total protein were measured in the blood samples and heart rates and finishing positions were recorded. Statistical analysis included paired t tests and Spearman's rank correlation coefficient. RESULTS: Of the 19 horses enlisted, only 16 horses completed the ride. Of these 16, another 2 were disqualified at the last veterinary check. When the 16 horses were considered, precompetition heart rate, but not ACE, was correlated with finishing position. When only the 14 horses that were classified were considered, the association disappeared. ACE activity was similar before and after competition. CONCLUSIONS: Precompetition ACE activity in endurance horses competing in an 80 km event was not associated with either finishing position or heart rates before or after competition, indicating that the enzyme is not a good predictor of performance in this form of equestrian competition. Endurance competition did not significantly alter ACE activity in this group of horses.

Disease suspected to be caused by Ross River virus infection of horses.

Ross River Virus (RRV) was believed to be the cause of acute illness in four horses around the Bellarine peninsula in south-west Victoria, Australia. The horses presented with clinical signs including petechial haemorrhages, lymphadenopathy, distal limb swelling and reluctance to move. Fibrinogen was also elevated in three of the four horses. Whilst no virus was isolated, serological testing revealed elevated RRV IgM titres in all horses indicating acute infection. The outbreak occurred at a time when a known RRV vector, the mosquito Aedes camptorhynchus was recorded at very high levels in the region. This report is one of very few to attribute specific signs of disease to RRV in horses in conjunction with serological evidence of infection.